The present invention relates generally to spindle motors in disc drives, and more particularly to the shielding magnetic flux from the spindle motor in the direction towards the printed circuit board assembly (PCBA).
In a disc drive, there consist of a multiple number of discs mounted on a spindle. The spindle is a motor with a circular base where permanent magnets are disposed in a radial manner about the center of the base forming a concentric circular structure. Between the permanent magnets copper wires are wound to form a stator winding such that a current passing through the copper wires would produce magnetic flux which will interact with the magnetic flux of the permanent magnets. In the center of the circular structure of the permanent magnets is a shaft secured to the base of the spindle. The shaft is fitted with ball-bearings to facilitate rotation about the center of a hub. The hub is press-fitted onto the shaft. The assembled hub rotates when the magnetic fluxes interaction produce a resultant force tangential to the circular arrangement of the permanent magnets. A printed circuit board assembly (PCBA) is used to control signals from the processor to drive the motor and thus enabling the discs to rotate about the spindle. Information or data is stored on the discs through the use of transducers or a magnetic read/write heads to write and retrieve information on/from discs surface. The transducer is mounted on an actuator arm, which flies above the disc surface to write and retrieve data. The magnetic flux from the spindle motor tends to leak in all directions as well as in the direction of the PCBA on every excitation and this will interfere with the operation of the transducer.
In order to reduce this interference, attempts have been made to reduce the magnetic flux leakage from the spindle motor by providing magnetic shields. Existing prior art teaches the use of magnetic shields in the form of plates, coatings or ring guides to reduce the amount of stray magnetic flux from the spindle motor. The materials used in these prior art magnetic shields are either steel or iron. The magnetic shields in prior arts are mostly directed to shielding off interference of stray flux from transducers and disc surfaces. Therefore, these magnetic shields are located on the upper portion of the spindle. However, stray magnetic flux also affect the signals in the PCBA located at the base of the spindle motor. U.S. Pat. No. 4, 553, 183 describes the use of a magnetic shield disposed within the spindle motor as a base plate for reduction of magnetic flux leakage. The material used for the base plate is steel or iron. In this patent, the magnetic shield is an integral part of the disc drive directed at preventing stray magnetic flux from the spindle motor and transducer to interfere or erase information stored on the discs. The base plate provided in this patent is positioned above the stator which leaves stray magnetic flux in the direction of the PCBA unshielded.
The interference due to stray magnetic flux from the spindle motor with signals of the PCBA poses a problem for effective operation of data storage and retrieval. Due to such interactions of stray magnetic flux, the position error signals (PES) are affected and cannot be within desired thresholds.
There remains a need for an improved reduction of magnetic flux leakage from the base of the spindle motor to minimize interference of the operation of the PCBA. It will be evident from the following description that the present invention offers this and other advantages.
According to one aspect of the invention, there is provided a magnetic shield for a spindle motor in a disc drive which is made multiple layers of materials. The magnetic shield is integrated into the disk drive to reduce magnetic flux leakage to the printed circuit board assembly (PCBA). The multiple layers of materials include polyester, pressure sensitive adhesives and steel configured in a multiple number of ways. The magnetic shield is adhered to the base of the spindle motor of a disc drive such that it covers the base of the spindle motor exposing the physical contacts of the spindle motor to allow interface connection with the PCBA. The region of the magnetic shield surrounding the physical contacts has additional layers of materials, which are selected from a group of polyester, steel and pressure sensitive adhesives.
In another aspect of the present invention, there is provided a disc drive with different parts that includes a spindle motor, a printed circuit board assembly (PCBA) and a magnetic shield. The spindle motor has a base with physical contacts that are connected to the printed circuit board. The magnetic shield, of multiple layers of materials, is integrated to the spindle motor to reduce leakage of magnetic flux from the base of the spindle motor to the PCBA. The magnetic shield is adhered to the base of the spindle motor and the multiple layers of materials in the magnetic shield is selected from a group comprising polyester, pressure sensitive adhesives and steel. The region surrounding the physical contacts of the spindle motor is exposed for interface connection to the PCBA. There are numerous configurations of the layers of materials that would provide effective magnetic shielding. Additional layers of materials are integrated at the region surrounding the physical contacts. These additional materials are selected from a group comprising polyester and pressure sensitive adhesives.
In yet another aspect of the present invention, there is provided a disc drive that includes a spindle motor having physical contacts to connect to a printed circuit board assembly (PCBA) such that magnetic flux leakage from the spindle motor to the PCBA is reduced by integrating a magnetic shield to the base of the spindle motor.
The magnetic shield of the present invention is assembled using existing assembly process with minimum increase in cost. The simplicity of the design of the current invention also provides ease in assembly. The effective result of the present invention is shown in the following detailed description of the invention.